Bus switches manufactured with semiconductor technology are used for high-speed network routing and switching applications. Complementary metal-oxide-semiconductor (CMOS) transistors may be used for bus switches, with a p-channel and an n-channel transistor in parallel as a transmission gate connecting or isolating two networks attached to the sources and drains of the transistors.
However, some systems use both 5-volt and 3-volt signals. These mixed systems can output a 5-volt signal to a 3-volt bus switch. The 3-volt bus switch could potentially latch up if a p-channel transistor was used in the switch. Using only n-channel transistors for the bus switch is therefore desirable for 3 v/5 v systems.
One solution is to boost the gate voltage to an n-channel transistor that acts as a bus switch. The gate voltage can be boosted above the 3-volt power supply by a voltage-booster circuit. For example, the gate voltage can be boosted to 4.3 volts using a capacitive pump. See for example, U.S. Pat. No. 4,639,622 by Goodwin et al., assigned to IBM; U.S. Pat. No. 4,063,117 by Lagesen et al., assigned to National Semiconductor Corp.; and U.S. Pat. No. 4,704,706 by Nakano et al., assigned to Fujitsu Ltd.